The invention relates generally to telephone communications systems, and specifically, to detection of caller identification data when receiving a call from a third party while already engaged in a conversation with a second party.
It is well-known in the art to provide caller identification (CID) services for users of telephone communications systems such as public switched telephone networks. CID is conventionally implemented while a telephone set is on-hook by transmitting digital data indicative of a caller's identity when a call is received during the time period between rings. It is also known to provide CID when a party receives a call from a third party while off-hook, i.e., while already engaged in a call with a second party. Such a service is commonly known as caller identification during call waiting (CIDCW) or Type II CID.
Conventionally, and as dictated by Bellcore specifications, CIDCW is implemented by muting a user's telephone handset for a period of time, during which the CIDCW signaling occurs. One example of such a system is disclosed in U.S. Pat. No. 5,263,084, issued Nov. 16, 1993 to Chaput et al., the disclosure of which is incorporated herein by reference. The muting operation serves to shield the user from any exposure to the potentially harsh noise that results from transmission of digital data on a telephone line. The muting operation further serves to prevent the user's voice from corrupting the digital data during the transmission of the digital data from the telephone company central office to the user's customer premise equipment, as well as during the transmission of data, such as the acknowledgment (ACK) signal, issued from the subscriber unit to the telephone company central office during the initial CIDCW handshake.
While caller ID information is being received, the handset is muted and communications on the line are temporarily interrupted. However, muting of the handset provides no indication to the subscribers that communications are interrupted. One or more of the parties involved in the conversation may not be aware that communications have been interrupted, potentially resulting in misunderstandings between the parties.
Another caller identification system is described in U.S. Pat. No. 5,836,009, issued Nov. 10, 1998 to Diamond et al., the disclosure of which is incorporated herein by reference. Diamond et al. provides an alternative implementation which attenuates but does not mute the caller ID information signal. The call recipient hears the noise of the acknowledgment tone and the FSK modulated caller identification signaling, which provide an audible indication to the user that communications have been disrupted. In an attempt to reduce the extent to which the acknowledgment tone and FSK noise may be objectionable to the user, the Diamond et al. system includes an attenuator operating to reduce the volume of the signaling noise before that noise is emitted by the recipient's telephone handset speaker.
However, even with an attenuator in place, the user is still subjected to signaling noise, which may be perceived as harsh electronic beeps and noise. The fundamental nature of the noise may be objectionable to some users, regardless of its volume. Moreover, some users may misunderstand the nature of the noises, erroneously thinking that an equipment malfunction has occurred. Further, subscriber units which rely upon attenuation of the received caller ID signals may still rely upon a muting mechanism for the CIDCW acknowledge signal issued to the central office.